It is common in the electronics arts to form electronic assemblies containing many different electronic components attached to a board, such as a printed circuit board (PCB). A printed circuit board is typically comprised of an insulator (e.g. paper, plastic, glass, or the like) substrate having metalization placed on one or both surfaces. The metalization is provided by transfer techniques or by deposition and etching techniques.
A problem often encountered in circuit layouts is that of providing heat dissipation for high power components. An example of the heat to be dissipated by surface mount devices may be illustrated by an SO-8 package. The SO-8 has a thermal resistance in the range of 45.degree. C./watt. An SOT-23 has a thermal resistance in the range of about 220.degree. C./watt.
The heat problem is amplified by the need to place the circuit on as small a surface area as possible. This makes the thermal resistance of the board and its ability to dissipate heat very important.
In the past, various attempts have been made to reduce the thermal resistance of components mounted on circuit boards. Ceramic materials such as alumina or beryllia have been used as circuit board substrates. However, these are very expensive.
Another alternative is the use of stud mounted electronic components. These provide a metallic stud in the component package on which a semiconductor chip is mounted. The stud passes through a hole in the circuit board and attaches directly to an underlying heat sink. The problem with stud type packaging is that they are not useful for surface mount devices and it is difficult to provide for electronic isolation of the stud from the heat sink (typically located on a second surface of the circuit board).
A third alternative is the use of a hole in the circuit board through which a portion of the external heat sink may protrude. This would place the external heat sink in direct contact with the component or component package. However, this arrangement is not useful with many different types of components and often does not provide sufficient heat removal from plastic encapsulated components.
None of the foregoing techniques are suitable for electronic assemblies when very low cost is an important consideration, and particularly when surface mount components are desired.
Accordingly, it is an object of the present invention to provide an electronic assembly having enhanced heat dissipating capabilities which overcome the above deficiencies and provides the desired advantages.
A further object of the present invention is to provide an electronic assembly having enhanced heat dissipating capabilities which improve the transmission of heat from the source to a heat sink.
Another object of the present invention is to provide an electronic assembly having enhanced heat dissipating capabilities which reduce the resistance from the heat source to the heat sink.
Still another object of the present invention is to provide an electronic assembly having enhanced heat dissipating capabilities which is economical to produce.
Yet another object of the present invention is to provide an electronic assembly having enhanced heat dissipating capabilities which utilize surface mount electronic components.
These and other objects and advantages are achieved in accordance with a preferred embodiment of the invention described below.